# Comparative Proteomics Analysis Reveals Differential Immune Responses of Paralichthys olivaceus to Edwardsiella tarda Infection Under High and Low Temperature

## TL;DR

This study shows how different water temperatures affect the immune response of Japanese flounder to a bacterial infection, revealing distinct protein-level changes at 15°C and 23°C.

## Contribution

The study provides new insights into temperature-dependent immune responses in fish through comparative proteomics analysis of Edwardsiella tarda infection.

## Key findings

- High temperature (23°C) enhances endocytosis and complement activity in flounder immune response.
- Low temperature (15°C) increases histone levels and disrupts RNA transport during infection.
- Differential immune-related proteins were identified at both temperatures, forming distinct interaction networks.

## Abstract

The health of farmed marine fish, including the Japanese flounder (Paralichthys olivaceus), is severely compromised by temperature fluctuations and infections such as Edwardsiella tarda, resulting in significant economic losses. A previous study revealed that elevated temperature enhanced E. tarda dissemination in flounder tissues. However, the underlying mechanism has not been fully explained, especially the changes in protein level. This study utilized label-free proteomics to investigate the immune response of flounder to E. tarda infection under low (15 °C) and high (23 °C) temperature conditions. Multiple differentially abundant proteins (DAPs) were identified in each group. GO and KEGG analyses highlighted immune-related pathways and proteins, with key DAPs forming extensive interaction networks. Venn analysis revealed distinct responses: high temperature promoted endocytosis and complement activation, while low temperature increased histone levels and impaired RNA transport. These results enhance our understanding of how water temperature changes affect antibacterial immunity in fish.

Fluctuating water temperatures and bacterial pathogens such as Edwardsiella tarda pose a serious threat to mariculture, resulting in significant economic losses within the flounder industry. A previous study revealed that elevated temperature enhanced E. tarda dissemination in flounder tissues. However, the underlying mechanism has not been fully explained, especially the changes in protein level. In this study, label-free proteomics was utilized to investigate the impact of high temperature (23 °C) and low temperature (15 °C) on flounder immune response to E. tarda infection. Our results identified 317 differentially abundant proteins (DAPs) in the low-temperature group (LI-LC) and 302 DAPs in the high-temperature group (HI-HC). GO and KEGG analyses of DAPs revealed numerous immune-related proteins and pathways. Twenty-six key DAPs in the LI-LC group and twenty-seven key DAPs in the HI-HC group were further identified and formed extensive interaction networks, respectively. Through the analysis of key immune-related DAPs that were specifically identified in both groups via Venn diagram analysis, we demonstrated that the endocytosis capacity and complement activity were enhanced in the HI-HC group, while histone abundance and RNA transport function were, respectively, increased and severely interfered with in the LI-LC group. These findings highlight a clear divergence in the immune response of flounder to E. tarda infection between 15 °C and 23 °C, providing valuable insights into how temperature variation influences antibacterial immunity in fish.